1. Field of the Invention
This invention relates in general to apparatus for driving a tape reel mounted for rotation on a tape recorder; more particularly, the invention is concerned with an apparatus for driving a reel mounted for rotation in a removable container of the type which is used with a magnetic tape recorder.
2. Description Relative to the Prior Art
The invention has general significance as a concentric-type friction drive for the supply and takeup reels of a tape recorder. Concentric friction gearing per se dates back to the nineteenth century and was used in such large-scale machinery as sawmills. Such drives include an output wheel having flanges of unequal diameter mounted for rotation on the wheel about a common axis. The diameters of the flanges are so chosen as to define an annular recess into which a friction drive wheel rotatably fits without contacting the flanges. Each flange further includes a frictional surface for cooperating with the friction drive wheel. With the drive wheel rotating in one direction only, the output wheel will change its speed and direction of rotation by frictionally engaging the drive wheel with one or the other of the flange surfaces. Concentric gearing is used in the recording art to reversibly drive, for example, a record carrying turntable (U.S. Pat. No. 3,190,133). It also finds occasional use in the internal mechanism of a tape recorder to reversibly drive, for example, a capstan (U.S. Pat. No. 2,914,264).
Cartridges and cassettes for containing a length of tape which is wound on a reel are also well established in the prior art. Such devices customarily require that the reel in the cartridge, or each reel in the cassette, be driven by a distinct drive shaft which is provided as part of the recording machine. Consequently, as the cassette or cartridge is placed on the recording machine, the hub of the reel in the cartridge, or the hubs of each reel in the cassette, must be made to receive the driven spindle(s) of the recording machine. If the reels are coaxially mounted in the cassette, then the hubs too must be so disposed as to separably receive a coaxial pair of driven spindles.
Specifically to simplify the drive mechanism for reels mounted side by side in a cassette, Fundingsland (U.S. Pat. No. 3,908,931) provides a bidirectional drive mechanism where the hubs or reels are engaged by a single pivotally-mounted drive wheel which is part of the recording device. The wheel is inserted into the cassette through an access slot for selective, frictional contact with either the supply or takeup reel. Since the reels are mounted side by side in the cassette, it is necessary to reverse the drive wheel, in addition to pivotally shifting the wheel, to effect reverse tape movement.
While not so restricted, the invention acquires a special significance when it is used as a concentric-type friction drive for the supply and takeup reels of a coaxial-reel tape cassette. While not employing a concentric-type friction drive, Gonmori (U.S. Pat. No. 3,352,976) illustrates a previous proposal to frictionally drive a coaxial-reel cassette. Gonmori provides an opening in the cassette for inserting a drive shaft into a space left between the two reels; the shaft is made tiltable or otherwise adjustable so as to obtain selective driving contact with the edge of either of the two reels. In this arrangement the direction of feed of the tape depends on which of the two reels is driven. Thus the recorder may be shifted from "rewind" to either "record" or "play" and back again without reversing the motor. Mechanically, the Gonmori device is similar to a rim drive in that the driving forces are applied at some distance from the reels' axis. The unbalanced effect thus obtained is less than desirable and likely to require some compensation in the structure of the reels.
The present invention acquires further significance when used with a constant torque motor or negator type spring interdrive between the supply and takeup reels. The negator -- as described in U.S. Pat. No. 2,996,264 -- is a tight spiral spring of thin ribbon-like metal which tends to recoil itself with constant torque when unwound. The negator spring is in an unwound (pretensioned) position at the beginning of the recording cycle and causes the takeup reel to rotate a predetermined number of turns relative to the supply reel during a complete cycle. This predetermined number of turns is about equal to the additional turns that the takeup reel must rotate, compared to the supply reel, to wind upon itself one-half the total length of tape initially on the supply reel. During this interval, the rate at which the tape passes the transducer or recording head is regulated by the constant speed characteristic of the capstan drive although minimal capstan power is required to transport the tape. After one-half the tape has been wound on the takeup reel and winding proceeds further, the negator spring reverses itself and begins to unwind to its beginning (pretensioned) position. Now the supply reel rotates a predetermined number of additional turns relative to the takeup reel as the remainder of the tape is wound up. Consequently, the interdrive between the two reels functions to rotate both reels in the same direction but at different rates while substantially constant tension is maintained throughout the tape path.